Adjustable inductors



July 5, 1966 J. H. WALKER 3,259,861

ADJUSTABLE INDUCTORS Filed April 29, 1965 FIG INVENTOR. James J2.Wazlker United States Patent "ice 3,259,861 ADJUSTABLE INDUCTORS JamesH. Walker, Hermitage, Tenn., assignor to Aladdin Industries,Incorporated, Chicago, 111., a corporation of Illinois Filed Apr. 29,1963, Ser. No. 276,620 1 Claim. (Cl. 336136) This invention relates toadjustable or variable inductors, particularly for use at radiofrequencies.

One object of the present invention is to provide a new and improvedadjustable inductor which will be capable of precise adjustment and willmaintain its adjustment under all operating conditions.

A further object is to provide a new and improved adjustable inductorwhich is extremely compact yet is capable of providing a high inductancevalue.

Another object is to provide a new and improved adjustable inductorwhich is highly efficient and is adequately protected against vibrationand moisture.

Further objects and advantages of the present invention will appear fromthe following description, taken with the accompanying drawings, inwhich:

FIG. 1 is a longitudinal section of an adjustable inductor to bedescribed as an illustrative embodiment of the present invention, thesection being taken generally along the line 11 in FIG. 4.

FIG. 2 is a plan view of the inductor of FIG. 1.

FIGS. 3 and 4 are transverse sections, taken generally along the lines33 and 44 in FIG. 1.

As already indicated, FIGS. 1-4 illustrate an adjustable or variableinductor 1 which in some cases may also take the form of a transformer.The illustrated inductor 1 comprises a coil or winding 2 mounted on aspool or bobbin 3. When it is desired to provide a transformer ratherthan a simple inductor, two or more windings may be mounted on the spool3. As shown, the spool 3 is received around a generally cylindrical tubeor form 4. Both the spool 3 and the form 4 may be made of insulatingmaterial.

To increase the inductance and efficiency of the coil 2, and also toprovide magnetic shielding, the inductor 1 comprises a pair ofcup-shaped shell members 5 made of low-loss magnetic material such asvarious ferrite compositions, powdered iron, or the like. Such low-lossmagnetic materials will be well known to those skilled in the art. Eachof the cup-shaped members 5 may comprise a generally circular end wall 6formed integrally with a substantially cylindrical side wall 7. It willbe seen that each side wall 7 is formed with a flat annular end face 8.

The cup-shaped members are axially aligned and positioned opposite eachother so that the end faces 8 of the side walls 7 are in abutment witheach other. Thus, the cup-shaped magnetic members 5 define a space 9within the side walls 7 and between the end walls 6. The coil 2 isreceived within the space 9 so that the magnetic members 5 provide ahousing around the coil.

In this case, each end wall 16 is formed with an axial bore 10 which isreceived around the insulating tube or form 4. Thus, the magneticcircuit provided by the magnetic members 5 is interrupted by an air gapor space between the portions of the end wall 6 around the bores 10. Toprovide for adjustment of the inductance of the coil 2, a core or slug11 is movable axially within the coil 2. In this case the core 11 isslida=ble within the insulated tube 4 which supports the coil 2. Thecore 11 is preferably made of low-loss magnetic material, such asvarious ferrite compositions, powdered iron or the like. However, insome cases the core 11 may be made of a conductive material, such ascopper, silver-plated brass,

or the like.

3,259,861 Patented July 5, 1966 In order that the core 11 may beprecisely adjusted, the illustrated core is provided with a threadedstud 12 which extends axially from one end of the core. The other end ofthe illustrated core 11 is formed with a screwdriver slot 27, or someother tool receiving formation so that the core may be adjusted byinserting an appropriate tool through the lower end of the insulatingtube 4.

In the illustrated construction, the threaded stud 12 is screwed throughan internally threaded bore 13 in a supporting member or disk 14adjacent one end of the tube or form 4. Thus, the core 11 may beadjusted along the inside of the form 4 by rotating the threaded stud12. A flat end portion 15 may be provided on the stud 12 to receive aslotted wrench or other tool so as to facilitate the adjustment of thecore 11. It will be realized that the flat end portion 15 maybe replacedwith any other suitable tool receiving formation. I In this case, theinductor 1 is provided with a conductive outer housing 16 which servesas an electrostatic shield for the coil 2. The illustrated housing 16has a flat circular upper end wall, which is formed integrally with asubstantially cylindrical side wall 18. The lower end of the side wall18 may be open to provide for insertion of the various components of theinductor into the housing 16. A terminal supporting disk or plate 19 maybe mounted within the lower portion of the side wall 18. The illustrateddisk 19 has an opening 20 which is received around the insulating tube4. Two or more terminals or leads 21 may be mounted in the disk 19 forestablishing electrical connections to the end-s of the coil 2. The disk19 may be made of various plastics or other insulating materials.

To protect the inductor 1 against moisture and vibration, all unoccupiedspace-s within the housing 16 may be filled with a suitable pottingcompound 22 composed of insulating material. Such potting compounds willbe well known to those skilled in the art. The potting compound 22retains the form 4, the cup-shaped members 5, the supporting disk 14,and the terminal plate 19 within the housing 16. As shown to advantagein FIG. 3, the cup-shaped members 5 may be formed with slots 23 whichpermit the potting compound to fill the unoccupied space around the coil2 and within the cup-shaped members 5. Thus, the coil 2 is solidlyanchored within the cup-shaped members 5.

It will be seen that the end wall 17 of the housing 16 is formed with anenlarged circular opening 24 around the threaded stud or stem 12. Tolock the stud 12 after it has been adjusted, a threaded disk or nut 25is screwed onto the stud and is adapted to be tightened against thesupporting disk 14. The opening 24 is sufficiently large to receive thenut 25 so that the nut may be screwed into the opening. The nut 25 maybe made of a thickness corresponding to that of the Wall 17 so that thenut will be fully received or recessed within the opening 24 when thenut is tightened down against the disk 14.

To provide for easy operation by a suitable tool, the illustrated nut 25is formed with a pair of openings 26 spaced outwardly from the threadedstud 12. The points of a pair of tweezers or some other tool may beinserted into the openings so that the nut 25 may easily be tightenedand loosened.

The inductance of the coil 2 may be adjusted to the desired value byrotating the screw stud 12 so as to move the core 11 within the coil.Then the nut 25 may be tightened against the disk 14 to maintain theadjustment of the stud 12. In some cases, it may be desirable to clipoff the projecting upper portion of the stud 12 so that the stud willnot project to any substantial extent above the housing 16. The core 11may also be adjusted by inserting a screwdriver upwardly through theinsulating form 4.

Various other modifications, alternative constructions and equivalentsmay be employed without departing from the true spirit and scope of theinvention, as exemplified in the foregoing description and defined inthe following claim.

I claim:

An adjustable inductor, comprising the combination of a pair ofcup-shaped members made of low-loss ferrite magnetic material, each ofsaid members having a substantially circular end wall connected to asubstantially cylindrical side wall, each of said end Walls having an'axial bore therein, said cup-shaped members being positioned oppositeeach other with said cylindrical side Walls disposed end to end to forma generally cylindrical space Within said side walls and between saidend Walls, an insulating tube positioned Within said space and extendingthrough said axial bores in said end walls, a coil mounted on theoutside of said tube and disposed in said space within said cup-shapedmembers, a substantially cylindrical core made of low-loss ferritemagnetic material and movable inside said tube and within said coil forchanging the inductance thereof, a disc having one side engaging one endof said insulating tube, said disc having a threaded bore thereindisposed opposite the end of said tube and along the axis thereof, athreaded metal stud secured to and projecting from one end of said coreand threaded through said threaded bore in said disc for moving saidcore along the inside of said tube, a metal housing mounted around saidcup-shaped members and having an end Wall engaging said disc on theopposite side thereof from said insulating tube, a mass of pottingcompound filling said housing and occupying the spaces therein aroundsaid cup-shaped members and said insulating tube to retain said tube andsaid cup-shaped members in said housing, said end wall of said metalhousing having an axial opening therein around said stud, and a nutthreaded onto said stud and engageable With said disc for locking theadjustment of said stud, said axial opening in said end wall of saidhousing being larger than said nut for freely receiving said nut, saidnut having a thickness corresponding to the thickness of said end wallof said housing and being substantially flush With said end wall of saidhousing when said nut is engaged with said disc.

References Cited by the Examiner UNITED STATES PATENTS 2,422,303 6/1947Jacob et al. 336-136 2,623,940 12/1952 Templeman 336100 X 2,768,35910/1956 Side 336-87 X ROBERT K. SCHAEFER, Primary Examiner.

JOHN F. BURNS, Examiner.

W. M. ASBURY, Assistant Examiner.

